Unfortunately, we have at present but little particular knowledge of the correlation of psychical and physiological processes. We cannot, by the dissection of a brain, draw much in the way of valid and detailed inference as to the nature of the psychical processes which accompany its physiological action. Fortunately, however, on the other hand, there are certain physical manifestations which do aid us, and that not a little, in drawing inferences from the physical to the mental. For organisms exhibit certain activities, and from these activities we can infer to some extent the character of the mental processes by which they are prompted. We are wont, in observing the actions of our fellow-men, to draw conclusions (often, alas! erroneous) as to the mental processes which accompany them. We are ourselves active, and we are immediately conscious of the modes of consciousness which accompany our actions. Thus the activities of organisms give us some clue to their mental processes, and it is through observation of their physical activities that we gain nearly all that is of particular value concerning the mental activities of animals. These activities we shall have to consider more fully in a future chapter. In the present chapter we shall consider them only so far as they give us information concerning the perceptual world (or worlds) of animals, and the nature of the inferences which we may suppose animals to draw from the phenomena which fall within their observation. I think that, from the fundamental identity of life-stuff, or protoplasm, in all forms of animal life, and from the observed similarity of nerves and nerve-cells when nervous tissue has been developed, and again from the essential resemblance of life-processes in all animal organisms, we are justified in believing that mental or conscious processes, when they emerge, are essentially similar in kind. Exactly when they do emerge in the ascending branches of the great tree of animal life it is exceedingly difficult, if not quite impossible, to determine. And it is, I fancy, quite impossible for us so to divest ourselves of the complexity of human consciousness as to imagine what the simplicity of the emergent consciousness in very lowly organisms is like. But I think that we may fairly believe that some dim form of discrimination is the germ from which the spreading tree of mind shall develop.[GE]